Typically traditional, non-electronic NDT methods involve usage of test materials with color or florescence property, which either leak or change patterns of distribution around flaws or defects. The NDT industry has formed certain conventions in using certain colors and florescence involving these traditional methods.
Modern instruments using array probe technologies, including eddy current array (ECA) and ultrasonic phased array (PA) technologies, with color imaging capability and its ability to detect surface-breaking or near-surface flaws through relatively thin coatings, are ideal replacements to traditional, non-electronic NDT methods for productivity reasons as traditional methods require intensive surface preparation, coating removal (and re-application after test), and have no direct means to record archive results apart from taking on-site pictures.
Eddy Current Array technology detects most flaws found by the traditional methods, and returns a color image (the C-scan) displaying colors as function of a signal amplitude or phase. In the existing market, the color schemes employed with ECA technology was done by various manufacturers using rainbow-style color palettes, typically comprising green/blue as base color, then shades of green, red, yellow. In contrast, traditional NDT methods such as penetrant testing (PT) and Magnetic particle (MP), either visible or fluorescent, provide characteristic visual images where flaws show up in a color tone much different from the background color representing non-defect zones.
Examples of visible penetrant testing include red tone and pink/purple tone. Red tone testing has a background (good part) of white/light gray, and flaws highlighted with bright red tones Pink/purple tone testing has a background (good part) of white/light gray, and flaws highlighted with pink/purple tones.
Examples of fluorescent penetrant testing, which is performed in a dark room with a “black light”, include green/blue shades and purple/blue shades. Green/blue shades typically have a background of dark blue tones and flaws glow as bright green shades (fluorescent). Purple/blue shades typically have a background of dark purple tones and flaws glow as light blue shades (fluorescent).
Examples of visible magnetic particle testing include red and black powder testing. The background color of red and black powder testing, which can vary depending of the surface being tested, shows better contrast when it is pale. The red and black powder will reveal the defects as the powders cling to the flaw edges.
Examples of fluorescent magnetic particle testing include purple shades and blue shades. Fluorescent magnetic particle testing is performed in a dark room with a “black light”. In purple shades the UV lamp typically produces purple reflects on the background color and flaws glow bright blue-green as the fluorescent magnetic particles cling to the flaw edges. In blue shades the UV lamp typically produces blue reflects on the background color and flaws glow bright blue-green as the fluorescent magnetic particles cling to the flaw edges.
Understandably, it is desirable to provide modern instruments, such as eddy current array technologies with the capability of displaying colors or florescence in the similar fashion as those traditional, non-electronic NDT method does.